[gmx-users] DFLEXIBLE option

Justin A. Lemkul jalemkul at vt.edu
Tue May 10 14:02:22 CEST 2011

Kavyashree M wrote:
> Dear users,
>       I wanted to know when DEFINE = -DFLEXIBLE has to be used.
> its given in the manual that it has to be used when we require flexible
> water instead of rigid waters, so if I am using tip4p water model and
> OPLSAA force field, and i use DFLEXIBLE option in EM and not in
> position MD, is there anything wrong? Kindly clarify my confusion.

Flexible water should be only really be used during EM and not MD.  All the 
water models included in Gromacs were designed to be rigid.  Using "define = 
-DFLEXIBLE" helps EM proceed a bit further, but is not appropriate for running MD.


> Thanking you
> With Regards
> Kavya


Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080


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